Headscratcher of the week

Jeff Kell jeff-kell at utc.edu
Fri May 31 22:39:52 UTC 2013


OK, here's a wild guess from left-field.  Well, at least from left-field
where I made at least one game-saving catch :)

We had a similar case some years back, but it was a ramp-up in overall
traffic we were looking at.  If you're looking at latency, it could be
related to traffic (do you have traffic graphs?).

One particular user that was accustomed to Windows and trying to get
started with Linux was "playing games" with our NAT firewall.  Rather
than file a request with us for a static NAT and firewall openings for
their "new" Linux server, they discovered that as long as they generated
some internet traffic periodically, they could defeat the NAT
translation timeout, and essentially keep a static outside IP.

Problem was, they "crontab"ed a "ping" of an outside server to run once
a minute.  Just a "ping x.x.x.x".

Windows as we know defaults to only ping 4 times then quit.

Linux does not :)

So you might look for some "recurring scheduled event" on the customer's
end that might be cumulative rather than simply recurring.

Jeff

On 5/31/2013 6:25 PM, Mike wrote:
> Gang,
>
>     In the interest of sharing 'the weird stuff' which makes the job
> of being an operator ... uh, fun? is that the right word?..., I would
> like to present the following two smokeping latency/packetloss plots,
> which are by far the weirdest I have ever seen.
>
>     These plots are from our smokeping host out to a customer
> location. The customer is connected via DSL and they run PPPoE over it
> to connect with our access concentrator. There is about 5 physical
> insfastructure hops between the host and customer; The switch, the
> BRAS, the Switch again, and then directly to the DSLAM and then
> customer on the end.
>
>
> The 10 day plot:
> http://picpaste.com/10_Day_graph-YV3IdvRV.png
>
> The 30 hour plot:
> http://picpaste.com/30_hour_graph-DrwzfhYJ.png
>
>
>     How can you possibly have consistent increase in latency like
> that? I'd love to hear theories (or offers of beer, your choice!).
>
> Happy friday all!
>
>
> Mike-
>
>





More information about the NANOG mailing list